Abstract
Sensitization of aluminum alloys lowers the safety of watercraft and is costly to mitigate. The development of new probes for determining the level of sensitization in alloys has been in focus during the last decade. This article argues the importance of the further development of a probe relying on ultrasonic detection. At least three physical quantities (shear wave velocity, longitudinal wave velocity, and longitudinal wave attenuation coefficient) of AA5083 andAA5456 aluminum alloys show sensitivity to material modification due to heat treatment at different temperatures. Resonant Ultrasound Spectroscopy and Pulse Echo were used for the measurements. The quantities vary monotonically with the heat treatment time, which correlates with the degree of sensitization in the alloy. The rate of change decreases as saturation is approached, in agreement with nucleation and growth kinetics. The 20% change between the as-received and the fully sensitized states, measured for the attenuation of longitudinal waves at 5 MHz, is already orders of magnitude higher than what other techniques have been capable of detecting. Stronger effects at higher frequencies are likely; the closer the wavelength to the size of the precipitate, the larger the attenuation. Extensions to determine sensitization in other alloys may be possible.
